Feeling nothing, you decide that it's safe move on. However, just as you take the first step your gut emits a strange gurgle. Stopping, you look down at it. Everything seems normal.
You go on with your walk, and manage to get about five feet before you hear another gurgle, followed by the feeling of motion in your stomach. Inspecting it again, you could almost swear that it's puffed out just a little more. It's not until you start watching that you notice your gut actually expanding. You have no intention of getting yourself a beer belly, however, so you start to think. How do you stop this?
Your first thought is simple: punch it until it stops. Lifting your hand, you swing it at your gut with all the might you can muster... and promptly feel a rush of pain as the impact knocks the air out of you. You check to see if it worked. Apparently not - your stomach seems to have grown out at least two inches, and it shows no sign of stopping. Hell, at this rate you'll have much more than a little unwanted bulge.
Time for plan B: trying to throw it up. Unfortunately, there's only one way you're going to achieve that here. Opening your mouth, you jam your fingers down your throat. You gag, you cough... nothing comes out. You try again. Again, nothing. Apparently, the only way to get the stuff to stop is to cut it out, something you couldn't do even if you wanted to without a knife or something.
Having accepted that this... thing is going to make its home in there whether you like it or not, you just sit back and watch as your belly extends out to four inches... six... twelve? As it eventually stops, rounding off quite a bit, you see that your gut now strongly resembles that of a VERY pregnant woman (and, given that you've got some sort of living thing in there, that comparison probably isn't far from the truth).